The present invention relates to a liquid crystal display and method for manufacturing the same, and especially, to a liquid crystal display and method for manufacturing the same having liquid crystal molecules axially symmetrically aligned within each liquid crystal region of a liquid crystal layer divided into plural regions by a wall-like structure.
Heretofore, TN (twisted nematic)-type liquid crystal displays and STN (super twisted nematic)-type liquid crystal displays including nematic liquid crystal molecules were used as display devices utilizing electrooptical effect. Techniques aimed at widening the viewing angle of these liquid crystal displays are being developed actively.
One example of the technique for widening the viewing angle of the TN-type liquid crystal display is disclosed in Japanese Patent Application Laid-Open Publication Nos. 6-301015 and 7-120728. The applications disclose a liquid crystal display having liquid crystal molecules axially symmetrically aligned within each liquid crystal regions of a liquid crystal layer divided into plural regions by a polymer wall, the display so called the ASM (axially symmetrically aligned microcell)-mode liquid crystal display. According to the disclosure, the typical liquid crystal display has each liquid crystal region substantially surrounded by a polymer wall formed to correspond to each pixel basis. The ASM-mode liquid crystal display has liquid crystal molecules aligned axially symmetrically. Therefore, no matter what direction the observer views the liquid crystal display, the contrast will not vary greatly. In other words, the liquid crystal display has a wide viewing angle characteristic. The ASM-mode liquid crystal display disclosed in the above-mentioned patent publications is manufactured by performing a polimerization inductionxe2x80x94phase separation to a mixture of polimerized material and liquid crystal material.
The conventional method for manufacturing the ASM-mode liquid crystal display is explained with reference to FIG. 6 (prior art). First, a substrate manufactured by forming a color filter and an electrode on one surface of a glass substrate 21axe2x80x2 is prepared (step (a)). For simplicity, the electrode and the color filter formed on the upper surface of the glass substrate 21axe2x80x2 are not shown in the drawing. The method for manufacturing the color filter is explained later. Next, a polymer wall 6xe2x80x2 for axially symmetrically aligning liquid crystal molecules are formed, for example in a lattice-shape, on the surface of the glass substrate 21axe2x80x2 equipped with the electrode and color filter (step (b)). In this step, a photosensitive resin material is spin-coated on the glass substrate 21axe2x80x2 to which the electrode and color filter are formed. Then, the substrate is exposed through a photo-mask having a predetermined pattern, and then developed. Thereby, a lattice-shaped polymer wall 6xe2x80x2 is formed. The photosensitive resin material can either be negative or positive. Further, a resin material having no photosensitivity can also be used, though a step for forming a resist film must be added to the manufacturing steps.
On portions of the top of the polymer wall 6xe2x80x2 are formed pillar-like protrusions 8xe2x80x2, which are selectively formed on areas of the wall by patterning (step (c)). In the present step, photosensitive resin material is spin-coated, and then a photo-mask having a predetermined pattern is used to expose and develop the substrate and to form pillar-like protrusions 8xe2x80x2.
The surface of the glass substrate 21axe2x80x2 to which are formed polymer wall 6xe2x80x2 and pillar-like protrusions 8xe2x80x2 is coated with a vertical alignment agent 9xe2x80x2 formed of polyimide and the like (step (d)).
On the other hand, an opposing glass substrate 21bxe2x80x2 to which is formed an electrode is also coated with the vertical alignment agent 9xe2x80x2 (steps (e) and (f)).
The two substrates 21axe2x80x2 and 21bxe2x80x2 formed as above are adhered together, with the surfaces equipped with electrodes facing the inner direction, to form a liquid crystal cell (step (g)). The distance between the two substrates (cell gap; thickness of the liquid crystal layer) is defined by the sum of the height of the polymer wall 6xe2x80x2 and the height of the pillar-like protrusion 8xe2x80x2.
Liquid crystal material is injected to the gap formed to the obtained liquid crystal cell through vacuum injection and the like (step (h)).
Lastly, the liquid crystal molecules within each liquid crystal region 31xe2x80x2 are axially symmetrically aligned, for example, by applying voltage to the pair of electrodes being opposed (step (i)). The liquid crystal molecules 32xe2x80x2 within each liquid crystal region separated by the polymer wall 6xe2x80x2 are axially symmetrically aligned with a center axis 33xe2x80x2 (perpendicular to both substrates) shown by the broken line of FIG. 6(i).
The cross-sectional structure of the conventional color filter will now be explained with reference to FIG. 7. On the glass substrate 21axe2x80x2 are formed a black matrix (BM) 4xe2x80x2 for shading the space (blocking light) between colored patterns, and a colored resin layer 5xe2x80x2 colored to red (R), green (G) and blue (B) corresponding to each pixel basis. An overcoat (OC) layer 51xe2x80x2 having a thickness of approximately 0.5 to 2.0 xcexcm made of acrylic resin or epoxy resin is formed above the colored resin layer 5xe2x80x2 so as to improve the surface smoothness. Moreover, a transparent signal electrode indium-tin oxide (ITO) film 7axe2x80x2 is formed on the overcoat layer. The BM layer 4xe2x80x2 is typically formed of a metallic chromium film having a thickness of approximately 100 to 150 nm. Resin materials colored by dyes and pigments are used to form the colored resin layer 5xe2x80x2, and the thickness of the layer is typically approximately 1 to 3 xcexcm.
The color filter can be manufactured by utilizing a method of patterning, through photolithography method, the photosensitive colored resin layer 5xe2x80x2 formed on the substrate 21axe2x80x2. For example, by utilizing photosensitive resin materials each colored to red (R), green (G) or blue (B), and performing formation/exposure/development for each of the three photosensitive colored resins (three times in total), an R/G/B color filter can be manufactured. The methods for forming the photosensitive colored resin layer 5xe2x80x2 include applying liquid-phase photosensitive colored resin material (diluted with solvent) onto the substrate 21axe2x80x2 through spin-coating method, or transferring the photosensitive colored resin material in the form of a dry film to the substrate. By using the color filter formed as above to manufacture the ASM-mode liquid crystal display, a color liquid crystal display having a wide viewing angle characteristic is obtained.
However, the present inventors have discovered that the ASM-mode liquid crystal display and the method for manufacturing the same according to the prior art have the following problems. That is, though a wide viewing angle characteristic is obtained according to the conventional ASM-mode liquid crystal display, the structure of the ASM-mode display is complicated compared to the conventional TN or STN-type liquid crystal display. Therefore, the manufacturing steps and the manufacturing cost according to the ASM-mode display is increased, and relatively, the yield factor is decreased. Moreover, since the transmission rate of the panel directly above the polymer wall 6xe2x80x2 (for axially symmetric alignment) is low compared to that of regions where the polymer wall 6xe2x80x2 does not exist, it causes the brightness of the display to be reduced when the overlapping area of the polymer wall 6xe2x80x2 is dislocated from the black matrix 4xe2x80x2 (positioned to shade the space between the colored resin layers 5 of the color filter) and the pattern of the polymer wall 6xe2x80x2 does not fit within the black matrix pattern. Moreover, when the polymer wall for controlling the alignment of the liquid crystal molecules are formed to have a steep tapered angle against the layer formed thereunder, the alignment of the liquid crystal molecules near the polymer wall is disordered. This causes light to be leaked from the area near the polymer wall even when the whole panel is displaying black, and causes deterioration of contrast. Moreover, the overcoat layer equipped to the display to flatten the color filter surface absorbs light, and causes the brightness of the display to be reduced.
The present invention aims at solving the above-mentioned problems. The present invention aims at providing a liquid crystal display and the method for manufacturing the same having a wide viewing angle characteristic, a high contrast and bright display, that can be manufactured at low cost and with improved yield factor.
In order to solve the above-mentioned problems, the present invention provides a liquid crystal display comprising a first substrate unit including a first substrate, colored resin layers, and a black matrix for shading the space (blocking light) between the colored resin layers; a second substrate unit; and a liquid crystal layer sandwiched between the first substrate unit and the second substrate unit: wherein the first substrate unit further comprises a wall-like structure composed of the overlapped portion of a lattice-shaped structure and the colored resin layers, for dividing the liquid crystal layer into plural liquid crystal regions, and to axially symmetrically align liquid crystal molecules within each liquid crystal region.
Moreover, the present invention provides a liquid crystal display, wherein the colored resin layers are formed so that the areas that are not overlapping the lattice-shaped structure have flat surfaces.
The present invention further provides a liquid crystal display, wherein the lattice-shaped structure has a cross-sectional shape that is gradationally tapered from the first substrate.
The present invention further provides a liquid crystal display, wherein the lattice-shaped structure has a thickness that is equal to or greater than the thickness of the colored resin layer.
Moreover, the present invention provides a liquid crystal display, wherein the lattice-shaped structure is formed of a transparent photosensitive resin material.
Even further, the present invention provides a liquid crystal display, wherein the lattice-shaped structure also serves as the black matrix.
The present invention further provides a liquid crystal display, wherein the black matrix is formed of a black-colored photosensitive resin material.
The present invention provides a method for forming a liquid crystal display comprising a first substrate unit including a first substrate, colored resin layers, and a black matrix for shading the space between the colored resin layers; a second substrate unit; and a liquid crystal layer sandwiched between the first substrate unit and the second substrate unit; wherein the first substrate unit further comprises a wall-like structure composed of the overlapped portion of a lattice-shaped structure and the colored resin layers, for dividing the liquid crystal layer into plural liquid crystal regions, and to axially symmetrically align liquid crystal molecules within each liquid crystal region; the method including the steps of: forming a black matrix made of a metal film on the first substrate; forming a lattice-shaped transparent structure having a cross-sectional shape that is gradationally tapered from the first substrate by using a transparent photosensitive resin material and through photolithography method; and forming colored resin layers so that a portion of each is overlapped to the tapered portion of the lattice-shaped transparent structure pattern.
Moreover, the present invention provides a method for forming a liquid crystal display comprising a first substrate unit including a first substrate, colored resin layers, and a black matrix for shading the space (blocking light) between colored resin layers; a second substrate unit; and a liquid crystal layer sandwiched between the first substrate unit and the second substrate unit; wherein the first substrate unit further comprises a wall-like structure composed of the overlapped portion of a lattice-shaped structure and the colored resin layers, for dividing the liquid crystal layer into plural liquid crystal regions, and to axially symmetrically align liquid crystal molecules within each liquid crystal region; the method including the steps of: forming a lattice-shaped structure that also serves as the black matrix having a cross-sectional shape that is gradationally tapered from the first substrate by using a black colored photosensitive resin material and through photolithography method; and forming colored resin layers so that a portion of each is overlapped to the tapered portion of the lattice-shaped structure also serving as the black matrix.
(Function)
The function of the present invention will now be explained. According to the invention, portions of the colored resin layers overlapping the lattice-shaped structure function as the polymer wall that generates the force for controlling and axially symmetrically align the liquid crystal molecules. Since the thickness of the lattice-shaped structure is equal to or greater than the thickness of the colored resin layer, a polymer wall having at least the same thickness as the lattice-shaped structure is formed to portions where the colored resin layers overlap the lattice-shaped structure. By setting the thickness of the lattice-shaped structure to 1.0 xcexcm or greater, a sufficient alignment regulating force is obtained. According to the prior art liquid crystal display where the polymer wall is formed separately, the wall has to be positioned and formed accurately above the black matrix pattern. If not, the transmission rate of the liquid crystal cell is reduced, and the brightness of the display is deteriorated. However, according to one embodiment of the present invention, the black matrix also serves as the polymer wall (lattice-shaped structure), so there is no need to consider the alignment of the polymer wall and the black matrix. According to the invention, the manufacture margin of the display is increased, and the display brightness is maintained. According to another aspect of the invention, the lattice-shaped structure is formed by a transparent resin layer. In this case, there is a need to align the polymer wall (lattice-shaped structure) and the black matrix. However, since the black matrix is formed only to the space formed between the colored resin layers and not to other unnecessary areas, the deterioration of display brightness caused by forming the polymer wall is prevented. Moreover, since the cross-sectional shape of the lattice-shaped structure is gradually tapered from the substrate, the colored resin layers overlapping the lattice-shaped structure is also gradually tapered. If the slope of the polymer wall is steep, the alignment of the liquid crystal molecules near the substrate and the wall is disordered, and this may cause leakage of light. However, according to the present invention, the overlapped area of the colored resin layers and the lattice-shaped structure functioning as the polymer wall has a gradationally tapered cross-section that is not steep. According to the invention, the problem of light leakage is solved, and contrast is maintained at high level.
Moreover, since the surface of the colored resin layers other than the overlapping area is flat, solely the polymer wall generates the axially symmetric alignment force that acts to the liquid crystal. Therefore, it is easy to create a center axis of alignment to the center of each liquid crystal region divided by the polymer wall. For example, if the surface of the colored resin layer within each liquid crystal region is not flat, the liquid crystal molecules receive both the alignment force from the polymer wall and that from the uneven colored resin surface. This causes difficulty in fixing the axial position, and causes deterioration of the viewing angle.